The Antbird

Aug 31, 2008 Features / Columnists, Interesting Creatures in Guyana

A perched Antbird

Regarded as a non-migratory bird specific to both Central and South America, the antbird is said to be of a genera of more than 230 species.

Antbirds make up the family Formicariidae and some of the genera are grouped together to form subgroups. These include the antwren, antvireo, antthrush, antcreeper, antshrike, fire-eye, bare-eyes and bushbirds.
They range in length from 10 to 36 centimetres (four to 14 inches).

Typically, the male has plumage which can range from dark grey to black with white patches and the female has red to olive colour plumage. Both genders are, however, outfitted with heavy and often hooked bills.

Although they are small in size, antbirds possess rounded wings and strong legs but are regarded as weak fliers, thus they spend most of their time on the ground.

The songs and calls of antbirds are generally simple uncomplicated notes. Nevertheless they are long, distinctive and species specific, allowing fieldworkers researching antbirds to identify many species without seeing them.

Antbirds rely on their calls for communication, as is typical of birds in dimly lit forests. Most species have at least two types of calls, the loudsong and the softsong.

The functions of many calls have been deduced from their context. For example, some loudsongs have a territorial purpose, and are given when birds meet at the edges of their respective territories, or during the morning rounds around the extent of the territory.

Pairs in neighbouring territories judge the proximity of rivals by the degradation of the song caused by interference by the environment. In bouts of territorial defence the male will face off with the other male and the female with her counterpart.

Loudsong duets are also potentially related to the maintenance of pair bonds. The functions of softsongs are more complex, and possibly related to pair bond maintenance.

In addition to these two main calls, a range of other sounds are made. These include scolding and mobbing of potential predators.

The calls of antbirds are also used inter-specifically. Some species of antbirds and even other birds will actively seek out ant-swarms using the calls of some species of ant-followers as clues.

Most species in the antbird family are forest-living, although a few are found in other habitats. The most important part of their diet is insects and other arthropods, although small vertebrates are occasionally taken. Most species feed in the understory and midstory of the forest, with a few species feeding in the canopy and on the ground.

Many species join mixed-species feeding flocks, and a few species are core members. A minority of them specialize in following columns of army ants to eat the small invertebrates that leave hiding to flee the ants, and many other species may feed in this way, opportunistically.

Antbirds are monogamous and intensely defend territories. They usually lay two eggs in a nest that is either suspended from branches or supported on a branch, stump or mound on the ground.

Both parents share the tasks of incubation, brooding and feeding the chicks. After fledging there is a division of the brood between the parents, with each parent caring exclusively for one chick.

However, a number of this bird species are threatened with extinction due to human activities. The principal threat is habitat loss, as antbirds are neither targeted by hunters or the pet trade. They are vulnerable to habitat fragmentation and to increased predation in fragmented habitats.

It is said that some species communicate warnings to each other by exposing the white feather patches on their back feathers or shoulders.

As of April 2008, 38 species are considered near threatened or worse and therefore at risk of extinction by the International Union for Conservation of Nature.

A natural experiment in fragmentation occurred on Barro Colorado Island, a former hill in Panama that became an isolated island during the flooding caused by the creation of the Panama Canal.

Numerous species of antbird formerly resident to the area went extinct, in no small part due to increased levels of nest predation on the island.

While the species lost from Barro Colorado are not globally threatened, they illustrate the vulnerability of species in fragmented habitats and help explain the declines of some species. The majority of threatened species have very small natural ranges.